Fluid delivery systems which are capable of providing a controlled flow of liquid between two surfaces are required for various applications. One such application is the field of biological diagnostic assay devices for the rapid analysis of analytes which are present in biological fluids. Various types of such assay elements are known in the art. Generally, a sample of a biological fluid, e.g., plasma, serum, etc., is applied to the assay element and as a result of the interaction between an analyte of interest in the sample fluid and the reagent(s) present in the assay element a detectable change corresponding to the presence of the analyte is brought about. The detectable change can be a color change which may be evaluated visually or read spectrophotometrically such as with a densitometer. In another scheme based on the presence of fluorescent-labeled biological species a fluorescent output signal is generated and read spectrofluorometrically. In order to obtain accurate and reproducible results it is essential that the sample fluid be distributed uniformly throughout the assay element so that a uniform signal or color is provided for reading by the instrument.
Various techniques have been described in the art for uniformly distributing a sample fluid throughout an assay element. It is known, for example, to use for this purpose fibrous layers, woven cloth layers, membranes having substantially uniform porosity and uniformly porous layers which allow capillary migration to provide the uniform fluid distribution. Also, there are known techniques for distributing liquids between two surfaces by the use of capillary action and such techniques have been taught for use in conjunction with providing small amounts of a sample fluid to analytical assay elements. U.S. Pat. No. 4,323,536 discloses a diagnostic test device which includes a plurality of test elements each of which is supplied with sample liquid from a single liquid sample. The device comprises a first member, a second covering member, these members having opposing surfaces, and means for spacing the members apart a distance effective to induce capillary flow of liquid introduced between the surfaces and thus create a liquid transport zone. One or both of the surfaces may have a plurality of exposed grooves in order to control the liquid flow paths in the device. U.S. Pat. No. 4,233,029 discloses a similar liquid transport device which has a controlled capillary liquid flow zone.
The prior art liquid transport devices are not satisfactory in all instances. For example, in filling such small spaces with liquid there is often encountered a problem with forming undesired pockets of trapped air which can cause errors in the case of quantitative analysis of the sample liquid. Accordingly, there is a continuing need for liquid transport devices
It is therefore an object of this invention to provide a liquid transport system.
Another object is to provide a liquid transport system capable of efficiently controlling the flow of a liquid between two opposing surfaces
A further object of the invention is to provide a liquid transport system for providing a uniform distribution of a liquid sample to a biological diagnostic assay device.
Yet another object of the invention is to provide a diagnostic assay device for the rapid analysis of a fluid sample.